1. Field of the Invention
The present invention relates to the pulse control (repetitive or single-shot) of one or several MOS-type switches or the like. The present invention more specifically relates to a voltage pulse generator to control such switches. In the present description, a xe2x80x9cMOS switch or the likexe2x80x9d designates any switch to be controlled by a voltage level such as, for example, MOS transistors or IGBTs. The present invention more specifically relates to the control of such switches used in the field of power regulation to control the operation of industrial or household equipment. In such a field, power semiconductor components switched to effect a so-called conduction angle control (or phase control) in which a power switch is only turned on for a portion of the duration of each halfwave or of one halfwave out of two of the supply voltage are often used. Such systems are currently used in the field of domestic lighting to form light dimmers, and in many other applications to provide power controllers.
2. Discussion of the Related Art
Power regulation by conduction angle control has the well-known disadvantage of generating, on the mains, harmonics due to the fact that the switch (for example, a triac) is turned on when a relatively high voltage is present thereacross. The harmonics cause electromagnetic disturbances and are a major problem. Various standards have been developed to require the manufacturer to avoid generating such disturbances. A simple way of avoiding the reinjection of harmonics on the mains consists of filtering them out. However, adding a passive filter to a controller is a serious handicap in terms of bulk, weight, and cost. To avoid this filter, it has also been envisaged to basically tackle the problem, by controlling the current variation speed (di/dt) upon switchings. Unfortunately, neither thyristors, nor triacsxe2x80x94which are ideal components for fabricating a variator due to their robustness, to their immunity against overcharges, to their switching ease and to their low on-state dissipated powerxe2x80x94allow control of di/dt.
FIG. 1 shows an example of a power switch with a controlled di/dt of the type to which the present invention more specifically applies. Such a circuit, preferably monolithic, includes two power components A and K and two control terminals G1 and G2. Switch 1 includes the parallel assembly of a MOS or IGBT-type component 2 and of a thyristor-type component 3, and means for inhibiting the thyristor-type component during a turn-on phase of the switch that is ensured by the IGBT-type component 2. IGBT power transistor 2 and power thyristor 3 are connected in parallel between terminals A and K. The anode of thyristor 3 and the collector of IGBT 2 are connected to anode A. The cathode of thyristor 3 and the IGBT emitter are connected to cathode K. In the embodiment of FIG. 1, a diode D is connected in antiparallel to thyristor 3 between terminals A and K. IGBT 2 is connected to a first control terminal G1 by its gate. The control of thyristor 3 is ensured by a high-voltage MOS transistor 4 (or by a second IGBT) connected between the anode of thyristor 3 and its gate. The source of high-voltage transistor 4 is connected to cathode K via a low-voltage MOS transistor M, the gate of which is connected to a second control terminal G2. The gate of transistor 4 is, preferably, connected to terminal G1. Alternatively, an impedance may be provided between the gates of transistors 2 and 4, or individualized signals may be provided for each of transistors 2, 4, and M.
Switch 1 of FIG. 1 is a one-way component. Thus, two switches of this type must be used in series-opposition to obtain a fullwave power controller. For example, the terminal A of a first switch 1 such as shown in FIG. 1 is connected to a first terminal of a load to be supplied, the other terminal of which is connected to a first mains voltage application terminal. The other mains voltage application terminal is then connected to the terminal A of a second switch 1, the terminal K of which is connected to terminal K of the first switch.
The operation of the circuit of FIG. 1 will be explained in relation with FIGS. 2A to 2C that respectively show, in the form of timing diagrams, voltage Vg2 on gate G2, voltage Vg1 on gate G1, and current IAK between anode A and cathode K of switch 1 of FIG. 1. A positive halfvave of voltage VAK between terminals A and K is considered. At a time tl, included in the first half of a halfwave of the mains voltage according to the desired conduction angle, gate G2 of transistor M is controlled to turn on transistor M, so that the gate and the cathode of thyristor 3 are short-circuited and that this thyristor cannot be turned on. At a time t2, subsequent to time t1 and also chosen according to the desired conduction angle, a voltage ramp having its slope controlled to obtain the desired di/dt is applied to gate G1 of IGBT 2. This ramp results for example from the application of a square or pulse signal through a fixed or variable impedance (of low power since it is a control signal), for example, a resistor or an RC filter. As soon as the voltage on terminal G1 exceeds a threshold value Vth, current IAK starts progressively increasing to reach a value depending on the mains voltage and on the impedance of the load at this time. Then, at a time t3, the signal on gate G2 is cut off to turn off transistor M. Since transistor 4 has been turned on by the ramp applied on gate G1 and on its own gate, the current flowing through transistor 4 triggers thyristor 3. Thyristor 3 turns on and its conduction is predominant over that of IGBT 2 since, generally, a thyristor exhibits a lower voltage drop than a MOS or IGBT power transistor. Then, at a time t4, the signal on gate G1 is cut off, so that IGBT 2 and transistor 4 definitively turn off. Thus, towards the end of the halfwave, at a time t5, current IAK falls under a hold value Ih and the thyristor turns off. Gate voltage G1 has been interrupted to prevent IGBT 2 turning on again.
Each of the IGBT 2 and the transistor 4 can be replaced by an IGBT or MOS or bipolar power transistor. Other monolithic power switch circuits with a controlled di/dt of the type to which the present invention applies are described in U.S. patent application Ser. No. 09/467,357 assigned to the present assignee, that is incorporated by reference.
As appears from the description of the operation of the power switch of FIG. 1, said switch must be controlled by two voltage pulses upon each halfwave of the A.C. voltage. Additionally, the pulse for controlling transistor M must have a control. The provision of such pulses results in several constraints. A first constraint is that said pulses are voltage pulses while it is more frequent, in the field of power variation, to control components (for example, triacs) with current pulses. A second constraint is that it is here necessary to control two switches (IGBT 2 and transistor M) while in conventional triac-based power variation circuits, a single gate is controlled. A third constraint as compared to circuits using triacs is that the control voltage must have a given polarity.
Of course, the solution that comes to mind to implement the control of such a power switch is to use a digital circuit (for example, based on a microprocessor) to generate, in a perfectly controlled way, the desired voltage pulses. However, such a solution has the disadvantage of being particularly expensive and of requiring an auxiliary power supply for a digital component.
An object of the present invention is to provide a voltage pulse generator that respects the previously-indicated constraints and that overcomes the disadvantages of a digital solution.
Another object of the present invention is to provide a pulse generation circuit, most components of which are integrable.
Another object of the present invention is to provide a particularly simple solution, of low bulk.
More generally, the present invention aims at providing a voltage pulse generator for controlling a power switch of IGBT or MOS type.
To achieve these and other objects, the present invention provides an analog voltage pulse generator, including a first break-over component of Shockley diode type to activate a rising edge of a pulse on an output terminal; and a second component of thyristor type to block the first component and deactivate the pulse.
According to an embodiment of the present invention, the pulse generator includes an RC cell between an input terminal and said first component to preset the time of occurrence of a rising edge of a pulse.
According to an embodiment of the present invention, the pulse generator includes a first resistor between said first component and said generator output terminal.
According to an embodiment of the present invention, the pulse generator includes a second resistor in parallel with the second component.
According to an embodiment of the present invention, the first component is formed of a first element of thyristor type associated with a second element of Zener diode type between its gate and its anode.
According to an embodiment of the present invention, the second component is a cathode-gate thyristor, the anode of which is connected to the cathode of the first component and the gate of which is connected, via a Zener diode, to a terminal of a capacitor adapted to being charged when the first component is on.
According to an embodiment of the present invention, the second component is an anode-gate thyristor adapted to being connected to an input of turn-on detection, by the rising edge of a pulse, of a MOS or IGBT-type component.
According to an embodiment of the present invention, a diode is interposed between the anode gate of the second component and the measurement terminal, a Zener diode being preferably interposed between the anode gate of the second thyristor-type component and the measurement terminal.
The present invention also provides a circuit for controlling a load adapted to being supplied by a high A.C. voltage including at least one power switch with a controlled di/dt including the parallel assembly of a MOS or IGBT-type components and of a thyristor-type component, with means for inhibiting the thyristor-type component during the turn-on phase of the switch, which is ensured by the IGBT-type component; and at least one voltage pulse generator of the above type for controlling with pulses the turing-on of the IGBT-type component.
According to an embodiment of the present invention, the means for inhibiting the component of thyristor type of the power switch is formed of a MOS-type transistor, the gate of which is also controlled with pulses, by means of said voltage pulse generator.
According to an embodiment of the present invention, the circuit includes two power switches, connected in series-opposition with each other and in series with the load to be controlled, each switch being associated with a sign of halfwaves of the A.C. voltage and being controlled by a pulse generator, the time of occurrence of a rising edge of a pulse with respect to the beginning of a halfwave of the A.C. voltage being set by means of a resistive element common to both generators and assembled in series with two storage capacitors respectively dedicated to one of the generators.
According to an embodiment of the present invention, the circuit includes two power switches, connected in series-opposition with each other and in series with the load to be supplied, each switch being associated with a sign of halfwaves of the A.C. voltage and the two switches being controlled by the same pulse generator associated with a rectifying means, the time of occurrence of a rising edge of a pulse with respect to the beginning of a halfwave of the A.C. voltage being set by means of a resistive element in series with a storage capacitor.
The foregoing objects, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.